1. Field of the Invention
This invention relates to a biaxially oriented container formed of a thermoplastic resin containing glass fibers.
2. Description of the Prior Art
Containers biaxially oriented by stretch blow molding thermoplastic resins such as polyethyleneterephthalate resin, polyvinyl chloride, etc. are excellent in gas barrier properties and mechanical strength as compared with containers obtained by blow molding and have a wide application not only for beverages but foods, cosmetics, medicines, etc.
Particularly, biaxially oriented containers formed of polyethyleneterephthalate resin increase in demand year after year but are low in glass transition point similarly to vinyl chloride resin. Even if the mechanical strength of containers is materially increased by biaxial orientation, there is a limitation in heat resisting property. In the case where the container is used as a container for contents whose filling temperature is above 70.degree. C., is has been necessary to impart the heat resisting property thereto by some means. When the container is used as a container for contents having pressure such as carbonated beverages even if the contents are low in filling temperature, there poses problems in that a bottom of a container is deformed due to an increase in internal pressure resulting from elevation of temperature not only to lose a self-supporting property as a bottle but result in explosion due to the shock at the time of falling.
As a means for solving these problems noted above with respect to the biaxially oriented containers, there has been employed a method for heating a stretch blow molded container at a higher temperature than the glass transition point to stabilize it against heat. Even by such a method, the heat resisting property is merely improved for a temperature in the vicinity of glass transition point but the durability for a higher temperature than the firstmentioned temperature and pressure under the high atmospheric temperature.
According to another approach, glass fiber is mixed into polyethyleneterephthalate resin in an attempt of enhancing the heat resisting property and the pressure resisting and further the gas barrier property and the like by said glass fiber. However, the moldability resulting from stretch blow molding of thermoplastic resin containing glass fibers varies with the content of glass fibers. The more content, the better various properties are obtained but conversely stretch blow molding becomes difficult to perform.
Accordingly, even the content of glass fibers has a limitation for reason in terms of molding, and in the content within the moldable range, the gas barrier property can be enhanced to some extent but satisfactory heat resisting property and pressure resisting property may not be obtained.